How to modify column default value in MySQL?

Let us first create a table −

mysql> create table DemoTable
(
   UserId int NOT NULL AUTO_INCREMENT PRIMARY KEY,
   UserName varchar(20) DEFAULT 'John'
);
Query OK, 0 rows affected (0.76 sec)

Let us check the description of table −

mysql> desc DemoTable;

This will produce the following output −

+----------+-------------+------+-----+---------+----------------+
| Field    | Type        | Null | Key | Default | Extra          |
+----------+-------------+------+-----+---------+----------------+
| UserId   | int(11)     | NO   | PRI | NULL    | auto_increment |
| UserName | varchar(20) | YES  |     | John    |                |
+----------+-------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)

Insert some records in the table using insert command −

mysql> insert into DemoTable values();
Query OK, 1 row affected (0.17 sec)

Following is the query to display all records from the table using select statement −

mysql> select *from DemoTable;

This will produce the following output −

+--------+----------+
| UserId | UserName |
+--------+----------+
| 1      | John     |
+--------+----------+
1 row in set (0.00 sec)

Here is the query to modify column default value. We have set the default UserName to Chris −

mysql> alter table DemoTable modify UserName varchar(20) DEFAULT 'Chris';
Query OK, 0 rows affected (0.19 sec)
Records: 0 Duplicates: 0 Warnings: 0

Let us check the description of table using desc command −

mysql> desc DemoTable;

This will produce the following output −

+----------+-------------+------+-----+---------+----------------+
| Field    | Type        | Null | Key | Default | Extra          |
+----------+-------------+------+-----+---------+----------------+
| UserId   | int(11)     | NO   | PRI | NULL    | auto_increment |
| UserName | varchar(20) | YES  |     | Chris   |                |
+----------+-------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)

Now insert some records in the table using insert command. Since we haven’t added a name, therefore the default “Chris” will get added −

mysql> insert into DemoTable values();
Query OK, 1 row affected (0.11 sec)

Following is the query to display all records from the table using select statement −

mysql> select *from DemoTable;

This will produce the following output −

+--------+----------+
| UserId | UserName |
+--------+----------+
| 1      | John     |
| 2      | Chris    |
+--------+----------+
2 rows in set (0.00 sec)